This invention relates to a method of preparing esters of pentavalent antimony, and more particularly, to a method of preparing metal salts of such esters from hydrated metal antimonates. The invention also relates to certain metal salts which are novel.
Various antimony compounds have been used as flame retardants for organic polymers and plastics. A commonly used compound is antimony trioxide, but its applications are limited because it is insoluble in water and other common solvents. Because of this insolubility, antimony trioxide is difficult to introduce within fibers and plastics. When applied to the outside of fibers and fabrics, the antimony trioxide is subject to mechanical wear and abrasion and is readily lost from the surface unless special binders are used. The use of binders, however, increases the stiffness of the fabrics and fibers further reducing the suitability of antimony trioxide as a flame retardant.
Glycerine and glycol esters of trivalent antimony are also known and have been suggested as being useful as flame retardants. However, these trivalent antimony esters generally are not soluble in polar organic solvents commonly used to dissolve polymers for spinning, and therefore cannot conveniently be incorporated into films or fibers of the polymers. Esters of pentavalent antimony have been prepared and these are soluble in polar solvents. Accordingly, they are well suited for processing organic polymers and can be conveniently incorporated into the polymers. Some of the esters are, however, highly sensitive to moisture. The salts of the esters are reported to be more resistant to moisture in U.S. Pat. No. 3,836,557.
A number of procedures for preparing esters of pentavalent antimony which are useful as flame retardants have been suggested in the art. In U.S. Pat. No. 3,873,451, a group of esters derived, at least in part from aliphatic polyhydroxy compounds having 2 to 6 carbon atoms and vicinal hydroxy groups are described. The esters are made by oxidizing antimony trihalide with nitric acid to form a hydrated oxide of pentavalent antimony which is reacted with an aliphatic polyhydroxy compound containing 2 to 6 carbon atoms and a vicinal hydroxyl group. A variety of water-soluble salts of pentavalent antimony glycol esters are described in U.S. Pat. No. 3,836,557 as being useful flame retardants for materials such as textiles or polymeric resins. A typical salt is tri(ethylenedioxy) hydrogen antimony (V), sodium salt. In addition to the metal salts, the patent describes guanidinium, ethylenediammonium and ammonium type salts of the esters and their use as flame retardants.
U.S. Pat. No. 3,657,179 describes antimony esters which are derived, at least in part, from alpha-hydroxy carboxylic acids. Such esters also are readily soluble in polar organic solvents and can be combined with spinning or casting solutions of organic polymers. The spun or cast polymer articles obtained from such solutions contain the dispersed antimony compound and are resistant to combustion.